In order to accurately demodulate data embedded in radio frequency signals, the received signal needs to be converted to a baseband frequency. In order to do this, the frequency of the transmitter should be matched at the receiver.
In practice, the radio frequency signal received by the receiver is distorted from the signal that was transmitted by the transmitter based on the channel conditions. In order to overcome this, estimations are made of the channel in an attempt to derive a gain and frequency from known data contained in the signal.
In low signal to noise ratio conditions errors in the estimated frequency can lead to undesirable fluctuations in a receiver's frequency control loop.